In an internal combustion engine of a vehicle there are provided an intake manifold for conducting intake air to cylinders and intake system components such as a throttle body.
More particularly, reference is here made to FIGS. 11 and 12. In both figures, the numeral 102 denotes an internal combustion engine with plural cylinders (i.e., four cylinders), the engine being mounted on a vehicle, and wherein 104 denotes a cylinder block, 106 denotes a cylinder head, 108 a cylinder head cover, and 110 an oil pan.
In the cylinder block 104 there is supported a crank shaft 114 with a crank pulley 112 fixed thereto, and there are also mounted, as auxiliary devices, a water pump 118 provided with a water pump pulley 116 and an alternator 122 provided with an alternator pulley 120. A driving belt 124 is entrained on the crank pulley 112, water pump pulley 116 and alternator pulley 120.
An intake manifold 126 and an exhaust manifold 128 are mounted to the cylinder head 106.
The intake manifold 126 is an integrally cast combination of a mounting flange 130 which is mounted to a side face of the cylinder head 106, a plurality of branch pipes 132 corresponding to the number of cylinders, and a surge tank 134 which suppresses intake pulsation.
A throttle body 136 is attached to one end face of the surge tank 134. It follows that the surge tank 134 and the throttle body 136 are located at upper positions of the branch pipes 132 which are curved and extend upward from the mounting flange 130.
As shown in FIGS. 13 and 14, the internal combustion engine 102 is supported elastically by left and right elastic mount members 138, 140 located on a principal axis of inertia G which is a central axis of inertia acting during operation of the engine 102, and forces acting in inertial directions are borne elastically by front and rear elastic mount members 144, 146 located on a member 142 which is disposed in the longitudinal direction (i.e., direction of movement) of the vehicle.
Known intake structures for use in such an internal combustion engine are disclosed, for example, in Japanese Patent Laid-Open Nos. 5-65857, 56-501056, 6-81735, 9-177623, 9-70720, 8-121273 and 9-4541.
In the intake structure disclosed in Japanese Patent Laid-Open No. 5-65857, an intake manifold is supported by an internal combustion engine through a stay member or brace. In the intake structure disclosed in Japanese Patent Laid-Open No. 56-501056, branch pipes are each formed in a predetermined curved shape to ensure both a required space and a length of the pipe. In the intake structure disclosed in Japanese Patent Laid-Open No. 6-81735, intake system components and branch pipes are formed as an integral structure to afford an advantage in point of space and attain a compact construction. In the intake structure disclosed in Japanese Patent Laid-Open No. 9-177623, a flange portion and branch pipes are formed of different materials to improve productivity. In the intake structure disclosed in Japanese Patent Laid-Open No. 9-70720, an intake manifold is constituted by a combination of composite materials to attain the reduction of weight for example. In the intake structure disclosed in Japanese Patent Laid-Open No. 8-121273, a mounting flange and a surge tank are formed by aluminum casting, while branch pipes are formed using iron, to avoid the occurrence of thermal strain for example. In the intake structure disclosed in Japanese Patent Laid-Open No. 9-4541, a resonator is disposed in a longitudinal direction of a fuel pipe and in proximity to the fuel pipe to prevent the transfer of heat from the internal combustion engine to the fuel.
In the conventional internal combustion engine intake structures, since heavy components such as a surge tank and a throttle body are disposed at upper positions of branch pipes not having a support rigidity, which positions are spaced apart from the principal axis of inertia G, vibrations are apt to occur in such heavy components during operation of the engine, which vibrations also exert a bad influence on electronic parts for example.
In the case where a support member such as a stiffener is used for improving the support rigidity of the surge tank and the throttle body, this results in an increase in the number of parts, in weight and in cost.
Moreover, the intake structure disclosed in above-mentioned Patent Laid-Open No. 5-65857 requires a large stay member; the one disclosed in above-mentioned Patent Laid-Open No. 56-501056 is disadvantageous in that since the surge tank used therein is disposed at an upper position, vibrations are apt to occur, weight is heavy and the freedom of layout is low; the one disclosed in above-mentioned Patent Laid-Open No. 6-81735 is disadvantageous in that since the surge tank used therein extends in the longitudinal direction of the internal combustion engine, not only an increase in size results, but also the distribution of air to cylinders is apt to become non-uniform; the intake structures disclosed in above-mentioned Patent Laid-Open Nos. 9-177623, 9-70720 and 8-121273 require a stay member for supporting the throttle body; and the one disclosed in above-mentioned Patent Laid-Open No. 9-4541 is disadvantageous in that the use of a resonator causes an increase in size.